Medical instrument sterilization container

ABSTRACT

The specification discloses a medical instruments sterilization container (10) which includes a housing (12) and a removable lid (14). A removable tray (16) is adapted to hold various medical instruments to be sterilized. The container is formed of a polymer of relatively low thermal conductivity, with a material having a relatively high thermal conductivity being added thereto in order to substantially increase the overall thermal conductivity of the container to absorb radiant heat and rapidly conduct that heat throughout the container to reduce condensate within the container.

RELATED APPLICATIONS

This is a continuation application of Ser. No. 208,730, filed June 17,1988, by Robert L. Nichols entitled "Medical Instrument SterilizationContainer", now U.S. Pat. No. 4,915,918, issued Apr. 10, 1990, which isa continuation application of Ser. No. 821,136, filed Jan. 22, 1986, nowU.S. Pat. No. 4,752,453, issued June 21, 1988, to Robert L. Nichols for"Medical Instrument Sterilization Container", which is a divisionalapplication of Ser. No. 668,090 filed Nov. 5, 1984, now U.S. Pat. No.4,617,178, issued Oct. 14, 1986, to Robert L. Nichols for "MedicalInstrument Sterilization Container."

FIELD OF THE INVENTION

This invention relates to sterile containers and more particularlyrelates to a medical instrument sterilization container with an offsetfilter arrangement.

BACKGROUND OF THE INVENTION

It is necessary in hospital and other medical environments to sterilizemedical instruments with steam or ethylene oxide. Various types ofsterilization containers for such medical instruments have heretoforecomprised muslin wraps, various paper wraps and sterilizationcontainers. When using the various types of wraps, medical instrumentsare placed in a tray, wrapped by a recommended procedure, taped, labeledand placed in a steam or ethylene oxide sterilizer. The steam orethylene oxide penetrates the wrap and kills the bacteria. Disadvantagesin the use of the sterilization wraps include the repeated expenses ofthe disposable wraps, potential punctures of wrapping materials therebycausing contamination, limited shelf life of the wrapped instruments andthe fact that the wraps are not stackable.

Various sterilization containers have been heretofore proposed whichprovide a hermetically sealed container with various filters whichprovide a relatively long shelf life, which cannot be easily punctured,which enable improved organization of the medical instruments and whichare stackable. Sterilization containers made of metal, such as stainlesssteel and aluminum, have been used, but are relatively expensive. Thesedevices are generally also opaque, thereby preventing a visual inventoryof the container interiors. Consequently, sterilization containers madeof plastics have been developed which can withstand the harshenvironments of the sterilization chamber and which are clear such thatinventories of the containers can be seen. Examples of such previouslydeveloped plastic sterilization containers are the Sterile-Case systemmanufactured and sold by Bemis Corporation and the Steri-Stor systemmanufactured and sold by Research Surgical Systems of Santa Ana, Calif.

Prior plastic sterilization containers have, however, suffered from theproblem of condensate accumulation on the internal and external surfacesafter sterilization. Although bacteria inside the container should besubstantially eliminated through the sterilization process, medicaltechnicians are trained to regard moisture as a breeding place forbacteria and thus condensate tends to cause technician acceptanceproblems, as well as providing an actual possible breeding ground forbacteria. In addition, the condensate increases the possibility forrusting and other deterioration of the metal instruments in thecontainer.

Steam sterilization units, whether they be gravity steam, pulsatingpressure steam or alternating vacuum and pressure or the like, allnormally have a drying cycle. During the drying cycle, steam is appliedto the jacket of the autoclave to create a hot environment and normallysome vacuum is applied to the chamber in order to lower the boilingpoint of the moisture. The drying cycle is utilized to evaporate themoisture in the sterilization container wrap or the like. However, clearor translucent plastic sterilization containers have a relatively lowthermal conductivity and thus do not allow the residual moisture to beevaporated within an economical time frame. The heat reaching thesterilization container within the sterilization unit comprises bothconductive and radiated heat. The conductive heat tends to heat thecontainer relatively slowly, in turn heating the moisture in thecontainer and creating slow evaporation. The radiated heat emanates fromthe jacket of the autoclave, but such radiant heat is not able to beutilized in evaporation of clear or translucent plastic containersbecause the majority of the radiative heat passes through the clearsurface of the plastic containers. The need has thus arisen for aplastic sterilization container which enables the sterilization ofmedical instruments and which also tends to prevent or eliminatecondensate from being formed on the interior surfaces thereof within aneconomical time frame.

SUMMARY OF THE INVENTION

In accordance with the present invention, a medical instrumentsterilization container comprises a housing dimensioned to receivemedical instruments for sterilization by gas or steam. A removable lidfor the housing enables access to the housing and seals with the housingto maintain the sterility of the housing interior. The housing is formedfrom a polymer of relatively low thermal conductivity and also includesmaterial having relatively high thermal conductivity in order that thehousing absorbs radiant heat to reduce condensate within the container.The high thermal conductivity material may be mixed in the polymer ormay be painted or coated on the container.

In accordance with another aspect of the invention, a medical instrumentsterilization container includes a housing having a bottom and sidewalls for receiving medical instruments for sterilization. A removablelid having an aperture therethrough sealingly fits over the housing. Ahousing bottom slopes to at least one location to bring condensate tothe one location. Filters are disposed in the aperture and the housingbottom at the one location. The filter passes air therethrough butprevents passage of contaminants into the housing.

In accordance with yet another aspect of the invention a medicalinstrument sterilization container includes a housing for receivingmedical instruments for sterilization. A removable lid sealingly fitsover the housing. A tray is removably disposed within the housing forsupporting the medical instruments. Apertures are formed through thebottom of the tray to drain condensate therefrom. The tray has domedportions between the apertures in order to facilitate draining ofcondensate.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theobjects and advantages thereof, reference is now made to the followingdescription taken in conjunction with the accompanying Drawings inwhich:

FIG. 1 is a perspective view of the present sterilization containershowing the lid in an exploded position;

FIG. 2 is a partially sectioned view of one-half of the length of thepresent sterilization container in conjunction with a front elevationthereof;

FIG. 3 is a top sectional view of a portion of the bottom of theremovable tray of the invention taken along section lines 3--3 in FIG.2;

FIG. 4 is an exploded view of one of the removable filters of theinvention;

FIG. 5 is a partial view of the housing showing the mixture of highthermal conductivity material within the clear plastic;

FIG. 6 is a partial view of the housing showing the high conductivityfibers mixed within the plastic; and

FIG. 7 is a partial view of the housing showing a high thermalconductivity material painted onto the inside surface thereof.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, the present sterilization container is identifiedgenerally by the numeral 10 and may be seen to include the housing 12and a removable lid 14. A removable tray 16 is received within thehousing 12 and is adapted to receive various medical instruments such asknives, scissors and the like.

A filter 18 is disposed through the lid 14 in order to allow the passageof heated sterile air or other sterilizing gases therethrough whilepreventing the passage of bacteria or other contaminants into theinterior of the container. Two additional filters, to be subsequentlydescribed, are disposed in the bottom of the housing 12. The tray 16includes removable metal handles 20 and 22 to enable easy withdrawal ofthe tray 16 from the housing 12. Apertures 24 are disposed through thetray 16 to allow the passage of steam and condensate therethrough. Metalclamps 26 are attached on both sides of the housing 12 and are manuallymovable in order to clamp against the side of the lid 14 in order tolock the lid to the housing. Suitable sealing surfaces are providedbetween the housing 12 and the lid 14 in order to provide an essentiallyairtight container when the lid is clamped to the housing. Handles 28are provided on opposite ends of container 12 to facilitate handling.

FIG. 2 illustrates a partially sectioned view of the sterilizationcontainer of the present invention. The filter 18 may be seen to includeapertures 30 which communicate with the atmosphere. A removable filter32 is clamped into place by a twistable cap 34. A sealing portion 36 isillustrated between the housing 12 and the lid 14. The clamps 26 may beseen to comprise a stationary portion 38 which is pivotally mounted bypivot 40 to a pivotal clamp portion 42. Manual depression upon a lip 44causes clamp 42 to be moved outwardly in order to accept the lid 14.When the lid 14 is in place, the movable clamp member 42 is moved byspring pressure to clamp against the lid in order to sealingly affix itto the housing.

FIG. 2 further illustrates pedestals 46 which elevate the bottom of thehousing 12. Also disposed on the bottom of the housing 12 are twoadditional filters 48 and 50 which are constructed in a similar manneras filter 18. Apertures 52 are disposed through the bottom of thehousing 12 in the filter area. A removable filter 54 is held tightly inplace by a twistable cap 56. A handle 58 is provided on the cap 56 toenable twisting into place. Catch members 60 inwardly extend from thebottom of the housing 12 for abutting with portions of the cap 56 inorder to maintain the filter 54 securely in place.

An important aspect of the present invention is that the bottom ofhousing 12 slopes downwardly toward both filter 48 and filter 50.Specifically, the bottom walls 62 and 64 each slope toward the locationof filter 48 in different directions. Thus, condensate or moisture inthe left-hand side of the tray of the housing 12 will move by gravity tothe filter 48. Likewise, moisture and condensate in the right-hand sideof the housing 12 will move by gravity along the similarly slopinghousing bottom wall to filter 50.

Referring again to FIG. 2, tray 16 includes apertures 24 as previouslynoted. An important aspect of the present invention is that the traybottom is domed at locations 66 between each aperture 24. This domedconfiguration causes condensate, steam and the like to run into theapertures 24 and prevents the accumulation of droplets of condensate orliquid on the bottom of the tray 16.

Referring to FIG. 3, which illustrates a section of one corner of a traytaken along section lines 3--3 in FIG. 2, the domed portions 66 areshown from a top view. It may be seen that each one of the domedportions comprises a rectangle with an aperture 24 located at the cornerthereof. The domes 66 are formed such that they slope at the cornersthereof to an aperture 24. Channels 68 are formed between adjacentapertures 24 to further assist in draining condensate or liquid throughthe apertures 24.

FIG. 4 illustrates in greater detail the construction of each of thefilters 18, 48 and 50. A twistable cap 56 includes four locking flanges70. The filter 54 is circular in shape and includes a plastic memberhaving plastic cross-members 72 which support the filter media 74. Thefilter media may be any suitable type of commercially available filterwhich allows the passage of air or other sterilizing gases therethroughbut which prevents the passage of contaminants such as bacteria. A tab76 extends from the filter to enable manual insertion and removal of thefilter. Filter 54 is disposable such that the filters may beperiodically replaced. Four locking members 60 are formed around therecessed area for receiving the filter 54 and the twistable cap 56.Apertures 52 extend through the bottom to enable steam or condensate topass therethrough.

In operation, the filter 54 is placed within the recessed area and thecap 56 is twisted such that the locking flanges 70 are tightly heldwithin the locking members 60. The cap 56 thus very tightly presses thefilter 54 against the side walls of the housing to seal the filter andprevent the passage of air past the edges thereof.

In the preferred embodiment, the present container is formed from asuitable plastic or polymer. As previously noted, clear or translucentplastic has a low thermal conductivity and cannot thus absorb enoughradiant heat to eliminate condensate within the housing during thedrying cycle of a sterilizer system in an economical time frame.Subsequently, the present invention contemplates the use of additionalhigh thermal conductivity materials in conjunction with clear plastic orpolymer in order to cause the absorption of sufficient radiant heat andrapidly radiate that heat through the container to eliminate condensatein an economical time frame such as within twenty (20) minutes. In thepreferred embodiment, the present invention contemplates the mixture ofhigh thermal conductivity materials 78, shown in FIG. 5, within theclear or translucent plastic. Alternatively, the invention contemplatesthe addition of a coating of high thermal conductivity materials to theclear or translucent plastic. It will be understood that various typesof high thermal conductivity materials may be utilized to accomplish theobject of the present invention. The following are examples which havebeen found to work well in practice and which provide a sterilizationcontainer having a resultant high thermal conductivity which tends toeliminate the formation of condensate therein when used in an autoclave.

EXAMPLE 1

A plastic is formed for use in a conventional plastic forming machine toprovide the present container by charging a non-fluxing type highintensity mixer with polypropylene copolymer, calcium carbonate and lowmolecular weight polyethylene and mixing to 105° C. Aluminum flakes arethen added and mixed for 15 to 20 seconds. The mixture is then fed to asingle screw compounding extruder and is melt mixed at a temperature of190° to 205° C. The resulting polymer is then pelletized as it comes outof the extruder. The resulting copolymer pellets may be utilized in aconventional forming machine to form the present container. The formulafor use with this example is listed below as a percentage by weight:

Polypropylene Copolymer: 55%-65% approximately

Aluminum Flake: 35%-50% approximately

Low Molecular Weight Polyethylene: 1%-5% approximately

Calcium Carbonate (CaCO₃): 0%-15% approximately

The polypropylene copolymer may comprise, for example, the copolymermanufactured by Eastman Company and noted as Tenite. Aluminum flakes maycomprise the aluminum flakes manufactured by Transmet Corporation andidentified as K-151. Suitable low molecular weight polyethylene ismanufactured by Allied Fibers and Plastics Company as AC-9. A suitablesource of calcium carbonate is Thompson, Wyman and Company under thetrade name Atomite.

EXAMPLE 2

A non-fluxing type high intensity mixture is charged with polysulfone,EBS, CaCO₃ and titanate and is mixed to 150° C. Aluminum flakes are thenadded and mixed for 15 to 20 seconds. The mixture is then fed to asingle screw compounding extruder and is melt mixed to a stocktemperature of 250° to 260° C. The formula for this mixture is listedbelow as a percentage by weight:

Polysulfone: 50%-60% approximately

Aluminum Flake w/ silane surface treatment: 25%-40% approximately

(EBS) Ethylenebisstearamide: 1%-5% approximately

Necalkoxy Titanate: 0.01%-0.1% approximately

Calcium Carbonate (CaCO₃): 0%-15% approximately

The polysulfone may comprise, for example, polysulfone manufactured byUnion Carbide as Udell T-1700. A suitable neoalkoxy titanate ismanufactured by Kenrich Petrochemicals under the trade name Capow 38/M.

EXAMPLE 3

A non-fluxing type high intensity mixture is charged with Polysulfone,titanate and EBS and mixed to 150° C. Carbon fiber 80, shown in FIG. 6,is added and the mixture is mixed to 160° C. The mixture is then fed toa single screw compounding extruder and is melt mixed at a stocktemperature of 250° to 260° C.

The formula for this mixture is set forth below as a percentage byweight:

Polysulfone: 90% approximately

Carbon Fiber: 10% approximately

Neoalkoxy Titanate: 0.01%-0.1% approximately

(EBS) Ethylenebisstearamide: 1%-5% approximately

The carbon fiber may comprise, for example, the fiber manufactured byUnion Carbide Specialty Polymers and denoted as Thornel (VMD).

EXAMPLE 4

A clear or translucent plastic container is formed by one of themixtures noted above such as polypropylene, calcium carbonate and lowmolecular weight polyethylene. A container is formed by conventionalforming techniques and the interior of the housing and lid is thencoated with semi-opaque high thermal conductivity material 82, shown inFIG. 7 such as a heat resistant paint or the like which contains carbonor the like. The container may be coated by painting, dipping or otherwell-known coating techniques. The clear plastic container mayalternatively be impregnated with carbon pigments under pressure.

Sterilization containers formed by any of the above examples will have arelatively high thermal conductivity. For example, the thermalconductivity of polysulfone plastic is approximately 1.7 BTU/HR/F²/°F/IN, while the thermal conductivity of aluminum is 10.8 and carbonfibers 60 BTU/HR/F² /°F/IN Plastic containers formed in accordance withthe present invention absorb substantially more heat through conductionand radiation and, therefore, heat faster and are more effective inmoisture evaporation as well as more effective in killing bacteria inmarginally operating steam sterilizers. The present container alsoenables the heat to more rapidly be transmitted to the entire interior,including the tray 16, thereby more effectively treating moisture orbacteria. The present construction of the container with the slopingbottom walls and domed portion of the removable tray also assists inpreventing the accumulation of moisture and condensation. It will thusbe seen that the present container provides a very efficient techniquefor sterilizing medical instruments and yet may be made in an economicalmanner.

Whereas the present embodiment has been described in detail, it shouldbe understood that various changes, alterations and substitutions can bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims.

What is claimed is:
 1. In a system for sterilizing medical instrumentsemploying a plurality of stacked sterilization containers where thereare at least upper and lower containers, each of said containerscomprising:a housing having a bottom and sidewalls for receiving a trayfor holding medical instruments; a lid having a centrally located raisedportion with an intake port therethrough; and two discharge ports formedin said bottom of said housing for draining condensate from saidcontainer, said discharge ports are arranged so that when said upper andlower containers are stacked condensate discharged from said dischargeports of said lid of said lower container, that is laterally spaced fromand below said intake port.
 2. The system of claim 1 wherein saidhousing bottom is sloped to each of said discharge ports.
 3. The systemof claim 1 wherein each of said discharge ports includes a filter. 4.The system of claim 1 wherein said intake port includes a filter.
 5. Thesystem of claim 3 wherein said filters are disposable.
 6. The system ofclaim 4 wherein said filter is disposable.
 7. The system of claim 6wherein each of said discharge ports includes a removable filter.
 8. Thesystem of claim 1 wherein said housing is constructed of an opaquematerial.
 9. The system of claim 8 wherein said material comprises amixture of polymeric material and other material having thermalconductivity higher than said polymeric material.